The British at the time of the American Revolution spoke with accents closer to how Americans speak now than how the British speak now, like the words you used as examples, Zoots. But outside of being a superfact, that doesn't really have much to do with anything. Maybe it's just because America is so goddamn rock n' roll and some American accents are really cool.

I'm equally baffled by people who sing in perfectly understandable English, but when they talk it's almost impossible to understand them because of their thick accent. I call this the Sharleen Spiteri syndrom.